Electrochemical sensors: theory and experiment

Abstract

A comparison is made of potentiometric and amperometric sensors. For amperometric sensors there are advantages in using the wall–jet system with ring–disc or packed-bed electrodes. Particular applications to the determination of proteins, root death, total iron and the concentration of NO₃^– are described. Enzyme electrodes using organic salts are capable of the direct oxidation of the enzyme itself. A theoretical description is presented. Experiments with glucose oxidase show that the transport of glucose through the membrane is the rate-limiting step. By contrast with a sensor for choline, using choline oxidase, we find that the transport of substrate through the membrane and the unsaturated enzyme kinetics are each partially rate-limiting. Electrodes, made of conducting organic salts, also oxidise NADH. For an ethanol sensor, using ethanol dehydrogenase, we find that the rate-limiting steps are those involving homogeneous enzyme kinetics.